The present invention relates to switch mechanisms for calculator type keyboards. Calculator type keyboards are utilized for a variety of computation and control functions. For example, they have been utilized in a television receiver to permit a viewer to select a particular channel and control such functions as volume, color and tint. Such an application is described in the "XL-100 Color Television -- The CTC-74 and CTC-81 Chassis" training manual published by the RCA Corporation, Indianapolis, Ind.
A calculator type keyboard includes an array of push buttons. Typically each push button corresponds to a decimal digit or command. It is often desired that a calculator type keyboard include switch mechanisms which are capable of directly converting decimal digits and commands into binary coded representations rather than indirectly by means of a logic circuit encoder so as to simplify its structure and reduce its cost. To directly encode all the decimal digits from 0 to 9 in, for example, the well-known and often employed binary coded decimal (BCD) format, it is necessary that at least one of the switch mechanisms associated with decimal digits be capable of actuating at least three contact closures when it is operated. In addition, it may be desirable to provide a contact which is closed after the closures of the code contacts in order to generate a signal signifying that data has been correctly entered and is ready for further processing. Further, it is desirable that a push-button switch mechanism with direct encoding features be capable of being simply and economically manufactured and incorporated in a calculator type keyboard, provide a tactile indication of its operation to an operator, and include self-cleaning contacts.
U.S. Pat. No. 3,952,174 discloses an array of solid concave disks, each connected to a thin sheet of conductive material so that they may readily be incorporated into a keyboard. As a disk is depressed it deflects in an "oil-canning" action thereby providing an operator with a tactile indication of its operation. However, because these switch mechanisms are arranged to make contact with only a single conductor, they are not useful for direct binary encoding. Furthermore, because the only motion permitted by the solid disk is along its axis, this switch mechanism does not provide a self-cleaning action.
In copending U.S. patent application Ser. No. 670,800 filed on Mar. 26, 1976 for the same inventor as the present invention, there is disclosed an array of switch mechanisms formed as an integral part of a conductive web so as to be economically manufactured and incorporated in a keyboard. Each switch mechanism includes intersecting support arms extending inwardly from the periphery of a cutout in the web. The support arms are deformed to form a dome-like contour. A plurality of contact blades extend outwardly from the intersection of the support arms. The web is spaced from a circuit board by a spacer with an aperture in general alignment with the switch mechanism. When the dome-like contour of the support arms is depressed, it "oil cans" thereby providing an operator with a tactile indication of its operation. As the contact blades come in contact with associated conductor areas formed on the circuit board, they slide along their surfaces thereby providing a contact cleaning action. The switch mechanism is relatively reliable because of the redundancy afforded by the plurality of contacts. However, because the contact blades cannot be made to consistently make contact at the same time, the mechanism is not particularly suited for direct encoding applications.
U.S. Pat. No. 3,941,964 issued in the name of Alan C. Yoder on Mar. 2, 1976 discloses a calculator type keyboard with individually mounted push-button switch mechanisms which, it is there stated, may be utilized to generate binary coded signals. Each switch mechanism includes a snap action diaphragm switch element having a center contact dimple with outward extending leg members and contact portions inwardly positioned with respect to the leg members. In order to support the diaphragm and provide code contacts at least some of the leg members of each switch mechanism engage terminal pads on the surface of an insulative board. When the switch mechanism is operated the normally opened contact portions are closed and code signals are applied to the terminal pads which engage the leg members. Therefore, to prevent the erroneous application of code signals to the terminal pads which engage leg members of other switch members, each switch mechanism must be electrically isolated from the others and cannot be connected by a common web member. Because the switch mechanism of the Yoder patent are separate units, they require individual placement and therefore are not well suited to be readily and quickly incorporated in a keyboard. Moreover, because in Yoder the legs are not part of the snap action diaphragm and are unsupported by a surrounding web, they do not contribute to any oil-canning effect. Still further, the oil canning deflection of the snap action diaphragm itself is inhibited by the center contact dimple.